ABSTRACT
We approach the subject of radiometry as that part of science and engineering that allows us to perform a measurement at a position of the observer while allowing us to draw conclusions about the quantity of radiation at another, possibly remote and inaccessible area. We use the radiation to allow us to transfer information from one point in space to another. To be able to draw a conclusion about the radiative state at a remote location, we must develop a clear concept of the quantities at the location of measurement and all processes that may change the radiation as it existed at its origin, including its modification upon propagation, incidence on an interface, propagation inside diverse media, and any mixture with radiative sources during the propagation. The modifications to the radiative signal arise as a consequence of scattering, absorption, reflection, and selective transmission. We introduce such important concepts as the BRDF, emissivity, Fresnel losses, Lambert’s law, and optical noise. As the radiation is a form of energy, we introduce energy-based terminology to describe its travel inside diverse beam-shaping environments, including windows, lenses, and other image-forming systems. We formalize the concepts of area, projected area, and solid angle to explain the limited amount of radiation collected from the source after travel. Due to the quantum nature of radiation, we present the radiative quantities also in terms of number of quanta in the optical signal. Finally, human visual system is characterized by specific radiation detection curves under two different conditions of illumination. We introduce the vision-based terminology, showing how energy-related quantities might be related to the vision-related terminology. Finally, we discuss how the signal may be determined quite well in a relative fashion, especially if using ratio technique. More precise absolute measurements require access to reference and calibrated standards. Finally, we discuss how the signal might be diminished due to noise acquired through the travel or during the detection process. We introduce the signal-to-noise as a performance measure. The radiometry chapter has been extensively rewritten. It includes 35 original figures to illustrate the basic concepts, with nine added for the second edition. Thirty-five new references have been included in this edition for further reading on radiometry and its diverse applications.
